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ASI294MC-Pro Sensor analysis & optimal exposure time

Posted: Tue Mar 24, 2020 12:55 am
I'm a little impressed and skeptical and wanted to confirm my optimal exposure time. I listened to Dr Robin Glover's talk - link and was very impressed. I'm a purist and think/hope I can get deep sky astrophotography done with out guiding. I'm currently shooting 5 minute subs, according to this presentation, I should be roughly at 90 seconds. After doing the sensor analysis, it's showing 28 seconds. I included some screen shots to help. I'm just wondering which is correct, I plan to experiment but being in North Jersey good sky conditions are hard to come by.

The 90 second calculation comes from the Optimal Sub length slide in Dr. Glover's presentation (at 50:28). A 2.5e read noise calls for 32 second sub length. I have 1.74e, so I used 30 seconds and multiplied by 3 since I'm using a OSC camera which gets me to 90 seconds.

ASI294MC-Pro. (Pixel size 4.63, 1x1 binning)
QE of 75%
Celestron Edge HD 11" with CGX-L Mount
F7 Focal Reducer
No filters
PHD2 guiding

Sky brightness (sky background calculator), Bortle number 5.3, F7.0, 4.63pixel at 75% QE gives me 1.74 e/pixel/s (I used 2 in the histogram)

Assuming a read noise limit of 5% and a total stack of 60 minutes here's what SharpCap Pro says:
Unity gain of 119: 283 seconds
Dynamic range Gain 121: 28.8 seconds (WOW, is this correct?)
Screen Shot 2020-03-23 at 8.44.59 PM.png
Screen Shot 2020-03-23 at 8.44.59 PM.png (509.74 KiB) Viewed 1169 times
Screen Shot 2020-03-23 at 8.45.19 PM.png
Screen Shot 2020-03-23 at 8.45.19 PM.png (486.04 KiB) Viewed 1169 times
Thanks in advance for any help/guidance - Jim